Researchers at Carnegie Institution for Science and Nanjing University published a study predicting that carbon and hydrogen — two of the most abundant elements in planetary interiors — can form a previously unknown atomic phase under crushing pressures, one in which hydrogen atoms travel only along helical pathways rather than moving freely in three dimensions, producing sharply directional electrical and thermal conductivity. The finding, published March 16 in Nature Communications, adds a new candidate mechanism to the decades-old puzzle of why Uranus and Neptune possess magnetic fields so unlike those of every other planet in the solar system.
Carbon Hydrogen Forms Helical Lattice at Terapascal Pressures
The three-author team — Dr. Cong Liu and Dr. Ronald Cohen of Carnegie Science's Earth and Planets Laboratory, along with Prof. Jian Sun of Nanjing University's School of Physics — used first-principles quantum simulations combined with machine-learning interatomic potentials to model carbon hydride (CH) at pressures ranging from 500 to 3,000 gigapascals and temperatures between 4,000 and 6,000 Kelvin. Those conditions correspond to the deep interiors of giant planets. At pressures above approximately 1,100 gigapascals, the simulations predicted a stable CH compound in which carbon atoms lock into a rigid helical framework while hydrogen atoms channel through that structure along spiral pathways, diffusing along a single axis and rotating around it, rather than moving freely in all directions.
"This newly predicted carbon-hydrogen phase is particularly striking because the atomic motion is not fully three-dimensional," Cohen said. "Instead, hydrogen moves preferentially along well-defined helical pathways embedded within an ordered carbon structure."
The compound also exhibits crystallographic chirality, forming distinct right- and left-handed mirror-image variants — an unusual structural property that further distinguishes it from previously known high-pressure phases.
Hydrogen Spirals Along One Axis: Directional Transport in Unfamiliar Phase
The newly predicted phase occupies a middle ground between states already known to physics. In a conventional superionic material — a category researchers have studied in planetary contexts for decades, principally in water ice and ammonia — one atomic species remains fixed in a crystal lattice while the other migrates freely through it in all three dimensions. The CH phase Liu, Cohen, and Sun identified adds a previously unrecognized variant: hydrogen remains mobile, but confined to helical channels within the carbon framework. The authors term this a quasi-one-dimensional superionic state, distinct from ordinary three-dimensional superionic matter and from solid or liquid phases.
As temperature rises past approximately 3,000 Kelvin, hydrogen eventually breaks free of its helical channels and diffuses in all three dimensions, transitioning into a standard three-dimensional superionic state, and ultimately into a fully fluid phase at higher temperatures still.
The directionality has direct consequences for how heat and electricity move through the material. In the quasi-1D phase, electrical and thermal conductivity along the axis of the hydrogen spirals is substantially higher than perpendicular to it. Planetary interior models have historically assumed materials conduct energy similarly in every direction; the new study challenges that assumption and suggests it may need to be revisited for materials at extreme pressures.
"Our work shows that even simple combinations of elements can organize into surprisingly complex states under extreme conditions," Liu said.
Magnetic Field Anomaly on Ice Giants Persists Since 1989 Voyager 2 Flyby
Uranus and Neptune have long resisted explanation from standard planetary physics. Voyager 2 — the only spacecraft to have visited either planet, conducting its Uranus flyby in January 1986 and its Neptune flyby in August 1989 — revealed that both planets' magnetic poles are dramatically offset from their rotation axes: by 59 degrees for Uranus and 47 degrees for Neptune. Earth's magnetic axis tilts just 11 degrees from its rotation axis. The ice giants' fields also originate from off-center locations deep within their mantles rather than from their cores. Standard dynamo models, which account well for Earth, Jupiter, and Saturn, have consistently failed to reproduce either anomaly. Several mechanisms have been proposed over the decades — including a 2024 study suggesting phase separation of planetary ices plays a role — but no consensus explanation exists.
Carnegie Simulations Stop Short of Claiming Direct Uranus Connection
The new study does not resolve the magnetic mystery. The authors explicitly note that the pressures at which the quasi-1D superionic CH phase forms — above 1,100 gigapascals — likely exceed those found inside Uranus and Neptune themselves. The paper states directly: "We do not claim any direct planetary or magnetic modeling relevance; instead, these findings suggest a plausible microscopic mechanism for anisotropic transport in dense molecular systems."
What the work does establish is a new theoretical mechanism: strongly directional electrical conductivity within a structured helical material could, if realized in planetary interiors at the right pressure and composition, influence the shape and tilt of a dynamo-generated magnetic field. Future work incorporating this mechanism into full dynamo simulations — or identifying related compounds that form at lower pressures — could make the connection more direct.
NASA Uranus Mission Formulation Starts 2027: New Interior Physics Feeds Mission Design
The research arrives as active planning proceeds for the first dedicated mission to Uranus since Voyager 2. NASA's 2022 Planetary Science Decadal Survey, issued by the National Academies of Sciences, Engineering, and Medicine, ranked a Uranus Orbiter and Probe as the highest-priority large planetary science mission of the decade, estimated at $4.2 billion. NASA is currently projecting formulation studies to begin in fiscal year 2027, with the goal of launching within the 2023–2032 decadal window. Interior structure and magnetic-field generation are central objectives of the mission concept. Theoretical work identifying new categories of atomic behavior — and new transport mechanisms — at planetary interior conditions directly feeds the scientific case for an atmospheric probe capable of sampling conditions well below the visible cloud tops.
Sub-Neptune Exoplanets May Reach Terapascal Pressures Where Phase Occurs
The study's implications extend to the growing catalog of known exoplanets. More than 6,000 confirmed exoplanets are now on record, and sub-Neptune-class worlds — those between the size of Earth and Neptune — are among the most common types detected. Many of these planets are significantly more massive than Uranus and Neptune and likely reach interior pressures well into the terapascal range where the quasi-1D superionic CH phase would be stable. The finding may therefore be more directly applicable to the interiors of those distant worlds than to our own solar system's ice giants.
Beyond planetary science, the helical hydrogen pathway described by Liu, Cohen, and Sun could carry implications for condensed-matter physics and materials science: the strongly directional conductivity characteristic of the phase may suggest design principles for engineered materials requiring anisotropic thermal or electrical transport — materials that conduct heat or electricity differently depending on orientation.
The solar system continues to supply conditions that Earth-based laboratories cannot yet replicate. Uranus and Neptune, at once familiar objects in astronomy textbooks and deeply mysterious in their interior physics, remain among the most productive puzzles in planetary science. That a combination as elemental as carbon and hydrogen can still produce atomic behaviors that surprise researchers is, for now, as much a statement about the limits of current models as it is a map of what future missions might find.
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